A computer system, such as a desktop-based or laptop-based computer system, may include multiple monitors, and a user of the computer system may define how an operating system of the computer system manages the multiple monitors. For example, a user may configure the computer so that the operating system treats one of the monitors as being an extension of the other. With this monitor extension configuration, the user may, for example, drag an object that is displayed on a first monitor to and beyond a display boundary of the first monitor to cause the object to be moved to (and displayed on) a second monitor. As another example, with this monitor extension configuration, a first monitor may be used to display email messages, and a second monitor may display attachments that are opened from the email messages. Other monitor configurations are possible. For example, the user may configure the computer system to display the same content on two monitors, or, for the case of a laptop-based computer system, the user may disable the laptop computer's built-in monitor, while enabling a larger standalone monitor that is connected to the laptop computer.